Background: Determining the appropriate disposition of emergency department (ED) syncope patients is challenging. Previously developed decision tools have poor diagnostic test characteristics and methodological flaws in their derivation that preclude their use. We sought to develop a scale to risk-stratify adult ED syncope patients at risk for serious adverse events (SAEs) within 30 days. Methods: We conducted a medical record review to include syncope patients age $ 16 years and excluded patients with ongoing altered mental status, alcohol or illicit drug use, seizure, head injury leading to loss of consciousness, or severe trauma requiring admission. We collected 105 predictor variables (demographics, event characteristics, comorbidities, medications, vital signs, clinical examination findings, emergency medical services and ED electrocardiogram/ monitor characteristics, investigations, and disposition variables) and information on the occurrence of predefined SAEs. Univariate and multiple logistic regression analyses were performed. Results: Among 505 enrolled patient visits, 49 (9.7%) suffered an SAE. Predictors of SAE and their resulting point scores were as follows: age $ 75 years (1), shortness of breath (2), lowest ED systolic blood pressure, 80 mm Hg (2), Ottawa Electrocardiographic Criteria present (2), and blood urea nitrogen. 15 mmol/L (3). The final score calculated by addition of the individual scores for each variable (range 0- 10) was found to accurately stratify patients into low risk (score, 1, 0% SAE risk), moderate risk (score 1, 3.7% SAE risk), or high risk (score. 1, $ 10% SAE risk). Conclusion: We derived a risk scale that accurately predicts SAEs within 30 days in ED syncope patients. If validated, this will be a potentially useful clinical decision tool for emergency physicians, may allow judicious use of health care resources, and may improve patient care and safety. © Canadian Association of Emergency Physicians.